Bench Power Supply Using a Computer’s Power Supply
For electronics engineers and hobbyists, the most important tool is a good bench power supply. But bench power supplies, which are used in R&D labs, are expensive. The rating of output is…
Know the mission before touching a wire.
Understand what you are making, prepare the right tools, and make the workbench safe.
Project details
Bench Power Supply Using a Computer’s Power Supply is a electronics project. For electronics engineers and hobbyists, the most important tool is a good bench power supply. But bench power supplies, which are used in R&D labs, are expensive. The rating of output is…
- Source pages
- 556-558
- Named parts
- 4
- Build goal
- Working, tested prototype
Tools you need
- Digital multimeter
- Wire stripper and side cutters
- Soldering iron with a fine tip
- Current-limited bench supply
Use eye protection, good lighting, and a clean insulated surface throughout the build.
Safety precautions
- Disconnect every power source before changing a connection.
- Check component polarity, pinout, and supply voltage twice.
- Use a current limit for the first power-up.
- This project may involve hazardous voltage. Work only with qualified supervision and proper isolation.
Gather, identify, and understand every part.
Use the standardized inventory, then open What's this? to learn each part's role, advantages, limitations, handling, and specifications.
What's this?Image, role, pros, cons, handling & specifications
Power supply
A power component supplies, converts, stores, or regulates energy for the project.
What it does hereIt must provide the documented voltage, polarity, isolation, and sufficient current safely.
Buy / compare this part ↗Advantages
- Stable power improves reliability
- Current limiting protects first tests
- Regulation reduces resets and noise
Limitations
- Wrong polarity can cause immediate damage
- Underrated parts overheat
- Mains circuits require qualified supervision
Handling
- Measure output before connection
- Use a fuse or current limit
- Insulate exposed conductors
Specifications to verify
- Use the exact model, value, package, and rating listed for Power supply; similar-looking parts are not always interchangeable.
- Confirm input/output voltage, current, polarity, connector, isolation, and thermal rating.
What's this?Image, role, pros, cons, handling & specifications
LM338K
A named project component whose exact role is defined by the source circuit and build guide.
What it does hereIt performs a documented electrical, control, interface, or construction function in this project.
Buy / compare this part ↗Advantages
- Selected for this project
- Can be checked independently
- Supports modular troubleshooting
Limitations
- Substitutes may differ
- Generic names can hide variants
- Pinouts and ratings vary
Handling
- Compare the received part with the source
- Keep it labelled
- Do not force connectors or adjusters
Specifications to verify
- Use the exact model, value, package, and rating listed for LM338K; similar-looking parts are not always interchangeable.
- Confirm dimensions, ratings, connection method, polarity, and environmental limits.
What's this?Image, role, pros, cons, handling & specifications
POWER LEARNING VIEWLM317
A power component supplies, converts, stores, or regulates energy for the project.
What it does hereIt must provide the documented voltage, polarity, isolation, and sufficient current safely.
Buy / compare this part ↗Advantages
- Stable power improves reliability
- Current limiting protects first tests
- Regulation reduces resets and noise
Limitations
- Wrong polarity can cause immediate damage
- Underrated parts overheat
- Mains circuits require qualified supervision
Handling
- Measure output before connection
- Use a fuse or current limit
- Insulate exposed conductors
Specifications to verify
- Use the exact model, value, package, and rating listed for LM317; similar-looking parts are not always interchangeable.
- Confirm input/output voltage, current, polarity, connector, isolation, and thermal rating.
What's this?Image, role, pros, cons, handling & specifications
MAXIMUM
A named project component whose exact role is defined by the source circuit and build guide.
What it does hereIt performs a documented electrical, control, interface, or construction function in this project.
Buy / compare this part ↗Advantages
- Selected for this project
- Can be checked independently
- Supports modular troubleshooting
Limitations
- Substitutes may differ
- Generic names can hide variants
- Pinouts and ratings vary
Handling
- Compare the received part with the source
- Keep it labelled
- Do not force connectors or adjusters
Specifications to verify
- Use the exact model, value, package, and rating listed for MAXIMUM; similar-looking parts are not always interchangeable.
- Confirm dimensions, ratings, connection method, polarity, and environmental limits.
Connect one verified path at a time.
Explore the named components and standardized signal flow, then use Source Check to verify exact physical pins, values, and topology before applying power.
Trace this circuit.
Bench Power Supply Using a Computer’s Power Supply: interactive parts, standardized terminals, responsive anchored wires, student explanations, and the original circuit reference in one shared system.
Trace before wiring
Follow power, ground, inputs, processing, and outputs in that order. Never guess a pin from package shape alone.
Connect with power off
Make short, labelled connections and share a common ground only where the schematic requires it.
Inspect every joint
Check continuity, polarity, adjacent shorts, and loose connections before the first power-up.
Open all source diagrams and build views 1 visuals
Confirm the hardware-only control path.
This project does not include firmware in the source. The circuit itself provides the required behaviour.
How to connect
- Match every controller label to the circuit view and source pin map.
- Join grounds before signal wires when separate low-voltage supplies are used.
- Keep motors, relays, pumps, and other loads on a suitable driver and external supply.
Common mistakes
Reversed VCC/GND, board-label versus GPIO-number confusion, missing common ground, and charge-only USB cables.
Troubleshoot
Disconnect loads, continuity-test one path at a time, then test with a current limit.
Software preparation
No IDE, board package, library, or firmware upload is required for this project.
If you add a programmable controller as an extension, document its pin map separately.
How to upload code
The original design is implemented entirely in hardware, so proceed after verifying the circuit and supply.
Assemble, deploy, test, and troubleshoot.
Use the complete source notes in build order, then pass the final checks before calling the project finished.
Build in functional stages
- Power and regulation
- Controller or processing stage
- Inputs and sensors
- Outputs and loads
- Enclosure and strain relief
Power up safely
- Inspect unpowered continuity first
- Apply the lowest safe current limit
- Measure supply rails before signals
- Add one load at a time
- Record expected and actual results
Work from simple to complex
- Confirm power, ground, polarity, and orientation
- Compare each pin with the source
- Test inputs separately from outputs
- Replace only one variable at a time
- Power off before every correction
Follow the documented instructions.
These notes come from this project's source and remain in their original order.
Project overview
Project build noteFor electronics engineers and hobbyists, the most important tool is a good bench power supply. But bench power supplies, which are used in R&D labs, are expensive. The rating of output is also a big deal. The most important thing that labs need is a variable DC supply that can go up to 30V and has a few amperes of current. Because the circuit is so complicated, it's not easy to make a power supply for a lab. To give out a lot of current, it needs big, heavy transformers and semiconductors. Use a computer power supply unit as an easy alternative (PSU). The PSU can be turned into a good bench power supply with a few changes.
Fig: Adjustable regulated power supply circuit Power up and testing To test a computer PSU without connecting it to the motherboard, connect the green wire to any of the black wires (ground wires). When the power supply is "on," the cooling fan should turn on. You can now use a multimeter to check the voltages of all the different wires in relation to the black wire. If all the voltages match the color code table, the power supply is working well. Checking the voltage of the grey wire, which is a PGS or power-good signal, is another way. It should be about +5V. When the power supply unit is opened You already know that computers use 230V AC power. Before you can open the PSU enclosure, you have to unplug its 230V power cord. After you take the cover off the PSU and unscrew the case, watch out for the big capacitors on the PCB. Wait a little while or use the right tool to discharge them. If you don't do this, you could get a shock from capacitors. Power supply with variable output
Use an LM338K or LM317 adjustable voltage regulator IC, as shown in Fig. 1, to turn the PSU into a variable power supply. 6. Connect +12V and -12V from the PSU to this circuit so that the maximum output ranges from 1.2V to +23V. But because the output current of -12V is only 500mA, the current output will drop to 500mA. Advantages of PSU 1. Very effective protection against short circuits 2. Protection from heat 3. Help for earth faults 4. In terms of voltage and current output ratings, the size is small. 5. Compared to other bench power supplies, this one is very cheap. Disadvantages 1. A complicated circuit that is hard to fix without the right knowledge 2. For repair, you might need an SMD soldering station.
You built Bench Power Supply Using a Computer’s Power Supply.
You followed the full workflow from understanding the mission to testing the finished project. That is a real engineering achievement - well done.
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